Williams Passenger Polarity

Off the top of my head, I'd connect one wire to the one feeding the existing light bulb, and the other to the tab that the bulb mount clips to, since that is connected to the truck mount->sideframes->wheels, therefore ground. The input side of the regulator doesn't specify polarity since it's switching 60x a second anyway

---PCJ

That sounds easy enough - if I'm understanding right.  The wire coming from the truck to the existing bulb goes to the positive input of the regulator.  Then a wire from the negative input of the regulator to the "frame" of the car?  

First off, if you're using the LED regulators, the wheels and roller connect to the AC connections on the regulator, and the polarity doesn't matter.  The DC+ obviously connects to the + side of the LED strip and the DC- connects to the - side of the LED strip.  With the Williams cars, the frame is the "wheels" connection.  Also note that the LED regulator works with AC or DC input track power of either polarity.

Note that since the regulator module employs a full-wave rectifier from track power, do not ground either of the DC outputs of the regulator, neither of them are at AC (frame) ground.  For your convenience, I've attached the documentation for the lighting regulator.

Pass Car Lighting Module Documentation.pdf

Straight from the source!  Thank you.  That clears everything up well.  I'll be sure to share my results when I get around to doing this.  Thank you!